Many hydrocarbonaceous mineral streams contain some small proportion of diamondoid compounds. These high boiling, saturated, three-dimensional polycyclic organics are illustrated by adamantane, diamantane, triamantane and various side chain substituted homologues, particularly the methyl derivatives. These compounds have high melting points and high vapor pressures for their molecular weights and have recently been found to cause problems during production and refining of hydrocarbonaceous minerals, particularly natural gas, by condensing out and solidifying, thereby clogging pipes and other pieces of equipment. For a survey of the chemistry of diamondoid compounds, see Fort, Jr., Raymond C., The Chemistry of Diamond Molecules,Marcel Dekker, 1976, as well as U.S. Pat. Nos. 5,019,660 to Chapman and Whitehurst and 5,053,434 to Chapman.
In recent times, new sources of hydrocarbon minerals have been brought into production which, for some unknown reason, have substantially larger concentrations of diamondoid compounds. Some of these diamondoid mixtures cause severe plugging problems in downstream processing equipment. Other diamondoid mixtures remain in the liquid phase under natural gas processing conditions and can be easily removed in a liquid knockout drum.
The problem of diamondoid deposition and plugging in natural gas production equipment has been successfully addressed by a controlled solvent injection process. U.S. Pat. No. 4,952,748 to Alexander and Knight teaches the process for extracting diamondoid compounds from a hydrocarbon gas stream by contacting the diamondoid-laden hydrocarbon gas with a suitable solvent to preferentially dissolve the diamondoid compounds into the solvent. U.S. Pat. No. 5,016,712 to Cullick and Roach teaches a method for locating the solvent injection point within the natural gas wellbore.
Further studies have revealed that separating diamondoid compounds into high purity fractions is complicated by their overlapping boiling points and relatively high vapor pressures. U.S. Pat. Nos. 4,952,747, 4,952,749, and 4,982,049 to Alexander et al. teach various methods of concentrating diamondoid compounds which dissolved in a solvent for, among other reasons, recycling the lean solvent fraction for reuse, and each of these processes produces an enriched solvent stream containing a mixture of diamondoid compounds. While these techniques meet the industrial need for a constant supply of relatively lean solvent for continuous recycle, the diamondoid-enriched streams rejected by these processes are not sufficiently pure to themselves be commercially useful. As mentioned above, conventional distillation of diamondoid-containing solvent mixtures is complicated by the fact that diamondoid compounds exhibit vapor pressures which are unusually high for their molecular weights.
U.S. Pat. No. 5,120,899 to Chen and Wentzek, which is incorporated by reference as if set forth at length herein, teaches a method of recovering the total diamondoid mixture without contamination using a high boiling point solvent which is injected into the natural gas wellbore.
Thus it would be desirable to provide a method for separating these recovered diamondoid mixtures into high purity fractions and components.